The in-situ measurements of conductive layer sheet resistance values during microelectronic device fabrication can provide valuable information for process control and real-time process end point detection applications. Example processes include chemical vapor deposition (CVD), processes for conductive layers such as tungsten, aluminum, copper; physical vapor deposition (PVD) of conductive layers; and plasma etch processes used for patterning conductors. Sheet resistance sensors may be used to monitor and control the etch or deposition processes in real time, or pre-process/post-process sensors, for example to be implemented in a vacuum load-lock chamber. These types of sensors are very useful for feedback process control as well as process and equipment diagnosis/prognosis.
There are several types of in-situ sensors which have been proposed in the past for CVD metal film thickness and or sheet resistance measurements. For example, an Eddy current sensor is a non-invasive in-situ (but not real time) sensor for pre-process/post-process measurements of metal film sheet resistance. Since this sensor is not real time, it cannot be used for many process end-point control applications.
A two-point probe employs two conductive wafer support pins to make electrical contact to the front side of the wafer edge within the metal deposition, for example tungsten CVD, process chamber. This is a contact type in-situ real-time sensor and can suffer from some limitations. This sensor depends on measurements of DC current and voltages between the two conductive wafer probe pins. As a result, its operation is sensitive to the contact resistance and/or potential values between the pins and wafer surface in the chamber. The probe contact resistance/potential and its temperature dependence can result in measurement uncertainties.
A microwave-based sheet resistance sensor is a non-invasive real-time in-situ sensor for metal sheet resistance measurements. Its operation is based on the use of microwaves (12-18 GHz) as a probe beam. This sensor, however, only provides an average sheet resistance value due to the large probe beam size. In other words, no real-time uniformity measurements may be made.
A fiber-optic scattering-base sensor is a non-invasive in-situ (but not real-time) sensor for pre-process/post-process measurements of CVD metal film thicknesses via surface roughness measurements. So once again, since the sensor is not real time it cannot be used for many real-time process end-point control applications.
Accordingly, improvements which overcome any or all of the problems are presently desirable.